The present invention relates to furnaces and more particularly to an electrically heated pressure furnace.
In producing and testing various material, e.g. sintered ceramics, it is often desirable to apply both high temperature and high pressure simultaneously, e.g. 100 atmospheres at 2200 degrees C. Further, it is typically desirable to provide a hot zone of relatively uniform temperature. Uniformity of temperature, however, is quite difficult to obtain at high pressures because of convection currents in the pressurizing atmosphere.
As will be understood by those skilled in the art, the pressure gradient which can drive a convection current for a given temperature differential increases with the density of the atmosphere, i.e. owing to pressurization. While convection currents would be minimal if the hot zone could be constructed as an entirely closed or sealed chamber, this is not practical in most instances since it is usually necessary to provide some clearance around feedthroughs for bringing electrical power to an electric resistance element within the hot zone. As is understood by those skilled in the art, the hot zone is typically enclosed by heat shields made up of spaced layers of tungsten sheet. These sheets are subject to considerable expansion and contraction during heating and cooling and thus it is impractical to provide a tight fit around the feedthroughs.
In constructions utilized heretofore, the necessary clearances resulted in very large heat losses which both increased the power required to maintain a given temperature and exposed elements outside the intended hot zone to excessively high temperatures, often resulting in damage and melting.
Among the several objects of the present invention may be noted the provision of an electrically heated high pressure, high temperature furnace which provides a relatively uniform hot zone; the provision of such a furnace which minimizes heat loss from the hot zone; the provision of such a furnace which requires minimal power to operate at high temperature and pressure; the provision of such a furnace which avoids damage to components outside the heat zone occurring due to convection heat loss from the hot zone; the provision of such a furnace which is highly reliable and which is of relatively simple and inexpensive construction. Other objects and features will be in part apparent and in part pointed out hereinafter.